A variety of Pharmaceutical dosage forms are known having one or more openings formed through an outer layer or layers on the surface of the dosage form. The openings generally allow release of contents from within an internal compartment of the dosage form to an external environment of use. Many different types of dosage forms that utilize such openings include, for example, osmotic controlled delivery systems as described in U.S. Pat. Nos. 3,854,770 and 3,916,899. In general, such osmotic systems utilize osmotic pressure to generate a driving force for imbibing fluid into an internal compartment formed, at least in part, by a semipermeable wall that permits free diffusion of fluid but not drug or osmotic agent(s). Typically, at least one exit orifice is formed through the semipermeable membrane. Following administration of the dosage form to a suitable fluid environment, such as the gastrointestinal tract or other body cavity or body tissue, fluid imbibition results in a deliverable drug formulation being released from within the compartment through the at least one exit orifice at a controlled rate.
Osmotic systems can be manufactured, for example, by forming an internal compartment containing an active agent and other ingredients, such as an osmagent and osmopolymer, into a solid or semisolid by ballmilling, calendaring, stirring or rodmilling and then pressing the internal compartment into a desired shape. In one embodiment, the internal compartment contains a drug layer and an osmotic material layer. Alternatively, a liquid therapeutic agent may be rendered into a solid or semi-solid shape, by for example, enclosing the liquid agent in a water-soluble capsule coated with an osmotic material layer. Finally, to prepare an osmotic delivery system, a semipermeable outer wall is applied to the solid or semisolid shape and at least one exit orifice is laser-formed through the semipermeable wall. The semipermeable wall is typically formed by dissolving the semipermeable wall material in an appropriate solvent, such as acetone or methylene chloride, and applying to the pressed shape by a suitable technique (U.S. Pat. Nos. 4,892,778; 4,285,987; 2,799,241).
After application of the semipermeable wall, the wall is dried and at least one exit orifice is formed in the device. Depending on the properties of the active agent and other ingredients within the internal compartment, and on the desired release rate of the active agent from the dosage form, at least one orifice is formed. The orifice(s) may range from a single large orifice containing an entire surface of the dosage form to one or more smaller orifices. Processes and apparatus for forming orifices in dosage forms using a laser beam have been described in the art, see for example, U.S. Pat. Nos. 4,063,064 and 5,783,793.
A problem encountered with the formation of exit orifices by laser drilling is the imprecise control of the depth of penetration by the laser beam. On the one hand, the laser beam must penetrate the outer wall to a depth sufficient to provide an exit orifice for operation of the device. On the other hand, it is undesirable for the laser beam to penetrate to a significant extent beyond the outer wall. For solid dosage forms, i.e., dosage forms having a compressed tablet core surrounded by a semipermeable membrane, penetration of the laser beam beyond the depth of the semipermeable wall may result in loss of some core material from the internal compartment. Although this loss can generally be minimized and controlled within a tolerance range, it would be highly advantageous to eliminate material loss. For liquid dosage forms, i.e., a liquid-filled capsule surrounded by an osmotic layer and coated with a semipermeable wall, penetration of the laser beam beyond the depth of the overlying layer(s) may result in piercing of the capsule wall resulting in unacceptable leakage of the liquid contents from the dosage form. Therefore, there exists a need in the art to eliminate material loss from a dosage form.